Question

已知x²-3x-1=0,求代数式2x³-3x²-11x+8的值

明确的答题过程。

Answer 1

x²-3x-1=0
x²-3x=1

原式=2x³-6x²+3x²-11x+8
=2x(x²-3x)+3x²-11x+8
=2x+3x²-11x+8
=3x²-9x+8
=3(x²-3x)+8
=3+8
=11

Answer 2

x^2-3x-1=0
x^2-3x=1

2x^3-3x^2-11x+8
=2x(x^2-3x)+3x^2-11x+8
=3x^2-9x+8
=3(x^2-3)+8
=3+8
=11